How to bind a buffer to a FILE pointer

Here's some example code for finding a string in a file via file mapping:

#include <iostream>
#include <algorithm>
#include <windows.h>

using namespace std;

int main()
{
     const char FileName[] = "c:\\testfile.txt";
     HANDLE hFileHandle = CreateFile(FileName,
          GENERIC_READ,
          FILE_SHARE_READ,
          NULL,
          OPEN_EXISTING,
          FILE_ATTRIBUTE_NORMAL,
          NULL);
     if (hFileHandle == NULL) {
          printf("Could not open file.\n");
          return -1;
     }
     DWORD FileSize = GetFileSize(hFileHandle, NULL);

     
     HANDLE hMapFile = CreateFileMapping(hFileHandle,    // Current file handle.
          NULL,                              // Default security.
          PAGE_READONLY,                    // Read permission.
          0,                                 // Max. object size.
          0,                                 // Size of hFile.
          NULL);            // Name of mapping object.
     
     if (hMapFile == NULL) {
          printf("Could not create file-mapping object.\n");
          return -1;
     }
     
     const char* lpMapAddress = (char*)MapViewOfFile(hMapFile, // Handle to mapping object.  
          FILE_MAP_READ,               // Read permission
          0,                                 // Max. object size.
          0,                                 // Size of hFile.
          0);                                // Map entire file.
     
     if (lpMapAddress == NULL) {
          printf("Could not map view of file.\n");
          return -1;
     }

     const char SearchData[] = "string";
     const char* FoundData = std::search(lpMapAddress, lpMapAddress+FileSize, SearchData, SearchData+strlen(SearchData));
     if (FoundData == (lpMapAddress+FileSize)) {
          printf("Could not find string.\n");
          return -1;
     }
     int FoundPosition = FoundData-lpMapAddress;

     cout << "Found item at position " << FoundPosition << endl;
     
     
     return 0;
}

>>>> 'setvbuf()' serves exactly that purpose:

setvbuf supplies a user-defined buffer to an opened - but not yet written or read - file.

If I understood the questioner correctly he has no file but only a buffer and wants to operate on that buffer using fread, fwrite, fseek ...

That would be similar to the relation of stringstream class to iostream or fstream classes.

I doubt that POSIX functions like fread, fwrite, fseek can be used on a buffer rather than on a file. The problem is that these functions/structs are C functions/structs that cannot be overloaded as it was possible withe the iostream (class) interface. Of course, you could write the buffer to a file, then read it again and call file streaming functions. If doing that on a RAM disk it would be fast but I don't believe it is worth the efforts.

Maybe you should post the 'algorithms' and interface you have. It is most likely you could easily convert these to iostream interface.

Regards, Alex